1. Field of the Invention
This invention relates to a pneumatic control system and alarm for adsorbent fractionaters. The control system and alarm is particularly suited for use with desiccant dryers and, more particularly, desiccant dryers of the relatively short cycle, heaterless type, such as disclosed, for example, in U.S. Pat. No. 2,944,627 to Skarstrom. Dryers of this type are currently marketed by several manufacturers around the world, including the present assignee. While controllers for heaterless dryers manufactured by the present assignee and others typically include electrical components, in some applications electricity may not be available or suitable as an energy source for the controller.
2. Description of the Prior Art
U.S. Pat. No. 4,205,967 to Sandman et al. and assigned to the present assignee discloses a pneumatic controller for use with desiccant dryers. A portion of the pressurized, product quality gas is employed as the energy source for the controller, with a time schedule for a series of reduced pressure, pneumatic valve control signals being generated based on time intervals determined by the length of time required to fill timing volumes to predetermined pressures. The time intervals may be varied by adjusting the sizes of orifices in the lines leading to the timing volumes. Pneumatic controllers of the type disclosed in the referenced patent have enjoyed success in applications where electric controllers are not suitable.